Corona and magnetic shielding structure for electrical transformers



Oct. 25, 1966 H. R. MOORE ETAL 3,281,745

CORONA AND MAGNETIC SHIELDING STRUCTURE FOR ELECTRICAL TRANSFORMERS Filed Sept. 10, 1963 2 Sheets-Sheet 1 i '5 |2 I I4 I Fig.4A. Fig.4B.

62 Mmmlil 54 52 Fig.5.

WITNESSES INVENTORS Raleigh J. Cossourt and Harold R Moore BYOELJ%%U ATTORNEY Oct. 25, 1966 H Rv MOORE ETAL 3,281,745

CORONA AND MA GNETIC SHIELDING STRUCTURE FOR ELECTRICAL TRANSFORMERS Filed Sept. 10, 1963 2 Sheets-Sheet 2 United States Patent Ofiice CORONA AND MAGNETIC SHIELDING STRUC Filed Sept. 10, 1963, Ser. No. 307,971 3 Claims. (Cl. 336-84) Our invention relates generally to shell type electrical transformers, and more particularly to shields for containing the magnetic flux of such transformers and preventing corona at the edges of the magnetic core of such transformers.

Transformer magnetic and corona shields of the prior art have disadvantages in regard to properly shielding the corners of the transformer magnetic core. Because of limited space in the coil window of a shelltype transformer, it has not been possible, without damaging coil insulation, to place corona shields exactly adjacent to the edges of the magnetic core of the transformer by driving the corona shields straight into the coil window. One prior art practice has been to make the magnetic shield narrower than the coil window to permit the shield to be inserted in the coil window.

Accordingly, it is a general object of this invention to provide a new and improved shield to be placed in the coil window of shell type electrical inductive apparatus.

It is a more particular object of this invention to prO- vide a magnetic shield to be placed in the coil window of a shell type electrical transformer which also reduces the electric stress which builds upon edges of the transformer core to thereby prevent corona.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

Briefly, the present invention accomplishes the above cited objects by providing a combination magnetic and corona shield which is divided into two or more parts. Each part of the shield includes a rigid member or plate to which is attached :a plurality of ferromagnetic laminations. A tubular electrical conductor is attached to one side of each of two of the rigid members. The rigid members are placed together in an edge to edge relationship and the shield is placed in the coil or phase window of a shell type electrical transformer. The shield is used between the tongue iron of the transformer core and the coils of the transformer. 'Ilhe rigid members are now forced apart laterally until the tubular electric-all conductors are substantially adjacent to the edges of the tongue iron of the core of the transformer.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the invent-ion, reference maybe had to the accompanying drawings, in which:

FIGURE 1 is a side elevational view, partly in section, of a shell type electrical transformer;

FIG. 2 is a vertical transverse sectional view of the electrical transformer of FIG. 1 taken along the plane IIII;

FIG. 3 is a fragmentary view of the transformer of FIG. 2 with the top combination corona and magnetic shield in its initial position;

FIG. 4A is a bottom plan view of a portion of the rigid member.

FIG. 4B is a bottom plan view of a portion of the combination corona .and magnetic shield; and

3,281,745 Patented Oct. 25, 1966 FIG. 5 is an end view of a portion of the combination corona and magnetic shield.

In FIGS. 1 and 2 of the drawings, there is illustrated an embodiment of our invention in which an electrical transformer 10 is provided with a laminated magnetic core 2. The laminated magnetic core 2 is of the well known shell type and has two loops. The magnetic core 2 partially encloses a plurality of electric coils such as low voltage windings 15 and high voltage windings 12. The electrical coils are so-called pancake windings which have a central window or phase opening 74 through which the so-called iron 7 of the laminated core loops pass. The pancake windings have substantially parallel side portions 82 connected by upper and lower end portions 84 which extend above and below the core 2. The transformer 10 is provided with a top end frame structure 3 located above the laminated magnetic core 2. A bottom section 6 of the transformer tank is provided with a flange as shown in FIGURE 1. The coils are installed in the bottom section 6 and the core 2 is stacked around the coils. The core 2 is supported around the outside by the flange 80 of the bottom section 6 of the transformer tank.

The end frame 3 is welded to the inside of a transformer tank top section 5 as shown in FIGURE 1. After the core 2 is completed, the top section 5 is put on and welded with weld 4 to the bottom section 6 at the flange 80. The distance between the bottom section flange 80 and the top end frame 3 is designed so that the core 2 is compressed and blocked in place when the top section 5 is pulled down and welded in place. The tongue iron portion 7 of the laminated magnetic core 2 is supported by a T beam 40. The high voltage winding, as shown, comprises a plurality of coils 12 centrally positioned in the transformer 10. Spacing members 13 are provided between the individual coils adjacent to insulation barriers 14. On opposite ends of the stack of high voltage coils 12, a group of low voltage coils 15 are provided with spacing members 16 and insulating barriers 17. Highlow spacers 18 are provided between the high voltage and low windings. End insulating barriers 22 are braced by the end frame 3 through the use of wedge members 21 so as to clamp the entire stack of high and low voltage coils against horizontal movement. Hardwood blocks such as blocks 33 may be used between the top of magnetic core 2 and the end frame 3. The blocks 33 may also be used between the flange 80 and the bottom of the ma netic core 2.

Our invention, as best seen with reference to FIGS. 2 and 3, includes a split pressure plate or rigid member 52 and groups of magnetic laminations 42 and 54. The lam-in-ations are attached to backup plates 62 and then fastened to the split pressure plate 52 by a method that be described later with reference to FIGS. 4 and 5. Between the lamination bundles and the windings are placed corona shields 48 and 64. It is well known to those skilled in the transformer art that corona will form most easily at sharp surfaces in .a transformer such as core edges. Therefore, the corona shields are constructed with smooth rounded surfaces, which preferably have a [generally elliptical cross-section, as shown in the drawings, to minimize this problem. The magnetic core 2 may be further modified to minimize sharp corners by using round surfaced members 66, 68 and 50 near corners of the core. The coil or phase window 74 may be partially filled with insulation members such as 46 and 58. Wooden wedges 60 may be used in the coil window 74 to compress the tongue iron 7 and provide support for the electric coils.

In the operation of our invention we place the split pressure plate 52 and the lamination bundle 54 along with the attached corona shields 64 into the coil window as a unit, as best illustrated in FIG. 3. We then wedge apart the split pressure plate 52 and attached laminations 54 as illustrated in FIG. 2 until the corona shields 64 are ladjacent to the corners of the tongue iron 7. An electrically conductive bridging member 56 may be used to cover the inside sharp edges of the spaced apart shielding bundles 54 to prevent corona fiorming at these edges. We have found German silver to be a suitable electrical conductor for this bridging application because of its ability to withstand the internal heat of the tarnsformer 10. A transformer core is usually built up by hand by stacking a plurality of laminations hence the bottom shielding bundles 42 may be placed in the desired locations on the T beam 40 and then welded to the T beam before the T beam is inserted in the coil window. The corona shields 48 associated with the shielding lamination bundles 42 may be Welded to the T beam 40 before the tongue iron 7 is built up.

Referring to FIGS. 4a, 4b and 5 in particular, there is illustrated means for attaching the magnetic shielding bundles 54 to the split pressure plate 52. We provide longitudinal slots 38 in the pressure plate 52. The lamination groups comprising the shielding bundle 54 are attached at one edge by any suitable means such as welding to relatively thin backup strips 62. The backup strips 62 are then attached to the split pressure plate 52 by means such as external welds 70. The plurality of longitudinal slots 38 provide further access to the backup strips 62 so that additional welds such as internal welds 72 may be provided between the backup strips 62, and the split pressure plate 52. We have found that for convenient assembly the lamination groups should be kept small. The lamination groups are staggered to prevent fiux crowding at the joints between lamination bundles.

It will, therefore, be apparent that there has been disclosed a combination magnetic and corona shield tor the coil window of shell type transformers which may be inserted in the coil window and then positioned adjacent to the outer corners of the tongue iron Without damaging the transformer insulation.

Since numerous changes may be made in the above described apparatus and different embodiments may be made without departing from the spirit thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

We claim our invention:

1. An electrical transiormerof the shell-form type comprising first and second magnetic core sections each formed of a plurality of stacks of metallic laminatizons arranged to define :at least one vertical opening, said first and second magnetic core sections being disposed in spaced side-by-side relation with the adjacent spaced portions of said first and second magnetic core sections forming at least one winding leg having top and bottom surfaces which have edges which define a portion of the perimeter of said at least one vertical opening in each of said first and second magnetic core sections,

electrical windings including a plurality of pancake coils disposed to encircle said at least one winding leg, and wedge means disposed between the top surface of the winding leg formed by said first and second spaced magnetic core sections and said pancake coils, said wedge means comprising first and second horizontally spaced pressure plate members disposed on the top surface of the winding leg fiormed by said spaced first and second magnetic core sections, respectively, first and second magnetic shielding means disposed on said first and second spaced pressure plate members, respectively, said first and second magnetic shielding means each comprising at least one bundle of perpendicularly stacked metallic laminations disposed with one edge on its associated pressure plate member, first electrically conductive means disposed to bridge said spaced first and second magnetic shielding means and contact certain edges of the perpendicularly stacked metallic lamin-ations, opposite the edges which are in contact with said first and second pressure plate means, and first and second tubular electrically conductive corona shielding means connected to said first and second pressure plate members, respectively, adjacent the edges of the top surface of the winding leg formed by said spaced first and second magnetic core sections which define a portion of the perimeter of the vertical openings in said first and second magnetic core sections. 2. The electrical transformer of claim 1 including support means disposed between the bottom surface of the winding leg formed by said first and second spaced magnetic core sections and said pancake coils, said support means comprising a support member having top and bottom surfaces, the top surface of said support member being disposed against the bottom surface of said winding leg, third and fourth horizontally spaced magnetic shielding means each comprising at least one bundle of perpendicularly stacked metallic laminations disposed with one edge in contact with said support means, second electrically conductive means disposed to bridge said third and fourth magnetic shielding means and contact certain edges of the perpendicularly stacked metallic laminations, opposite [the edges which are in contact with said support member, and third and fourth tubular electrically conductive corona shielding means connected to said support member adjacent the edges of the bottom surface of the winding leg formed by said spaced first and second magnetic core sections which define a portion of the perimeter of the vertical openings in said first and second magnetic core sections.

3. The electrical transformer of claim 1 wherein said first and second tubular electrically conductive corona shielding means are substantially eliptical in cross section.

References Cited by the Examiner UNITED STATES PATENTS 2,269,678 1/1942 Mauerer 29155.5 2,344,006 3/ 1944 Steinmayer 29155.5 2,370,045 2/1945 Ket-o 33684 2,942,215 6/1960 Bennon et al 336- 3,173,116 3/1965 Schneider 336-84 LEWIS H. MYERS, Primary Examiner.

ROBERT K. SCHAEFER, Examiner.

W. M. ASBURY, Assistant Examiner. 

1. AN ELECTRICAL TRANSFORMER OF THE SHELL-FORM TYPE COMPRISING FIRST AND SECOND MAGNETIC CORE SECTIONS EACH FORMED OF A PLURALITY OF STACKS OF METALLIC LAMINATIONS ARRANGED TO DEFINE AT LEAST ONE VERTICAL OPENING, SAID FIRST AND SECOND MAGNETIC CORE SECTIONS BEING DISPOSED IN SPACED SIDE-BY-SIDE RELATION WITH THE ADJACENT SPACED PORTIONS OF SAID FIRST AND SECOND MAGNETIC CORE SECTIONS FORMING AT LEAST ONE WINDING LEG HAVING TOP AND BOTTOM SURFACES WHICH HAVE EDGES WHICH DEFINE A PORTION OF THE PERIMETER OF SAID AT LEAST ONE VERTICAL OPENING IN EACH OF SAID FIRST AND SECOND MAGNETIC CORE SECTIONS, ELECTRICAL WINDINGS INCLUDING A PLURALITY OF PANCAKE COILS DISPOSED TO ENCIRCLE SAID AT LEAST ONE WINDING LEG, AND WEDGE MEANS DISPOSED BETWEEN THE TOP SURFACE OF THE WINDING LEG FORMED BY SAID FIRST AND SECOND SPACED MAGNETIC CORE SECTIONS AND SAID PANCAKE COILS, SAID WEDGE MEANS COMPRISING FIRST AND SECOND HORIZONTALLY SPACED PRESSURE PLATE MEMBERS DISPOSED ON THE TOP SURFACE OF THE WINDING LEG FORMED BY SAID SPACED FIRST AND SECOND MAGNETIC CORE SECTIONS, RESPECTIVELY, FIRST AND SECOND MAGNETIC SHIELDING MEANS DISPOSED ON SAID FIRST AND SECOND SPACED PRESSURE PLATE MEMBERS, RESPECTIVELY, SAID FIRST AND SECOND MAGNETIC SHIELDING MEANS EACH COMPRISING AT LEAST ONE BUNDLE OF PERPENDICULARLY STACKED METALLIC LAMINATIONS DISPOSED WITH ONE EDGE ON ITS ASSOCIATED PRESSURE PLATE MEMBER, FIRST ELECTRICALLY CONDUCTIVE MEANS DISPOSED TO BRIDGE SAID SPACED FIRST AND SECOND MAGNETIC SHIELDING MEANS AND CONTACT CERTAIN EDGES OF THE PERPENDICULARLY STACKED METALLIC LAMINATIONS, OPPOSITE THE EDGES WHICH ARE IN CONTACT WITH SAID FIRST AND SECOND PRESSURE PLATE MEANS, AND FIRST AND SECOND TUBULAR ELECTRICALLY CONDUCTIVE CORONA SHIELDING MEANS CONNECTED TO SAID FIRST AND SECOND PRESSURE PLATE MEMBERS, RESPECTIVELY, ADJACENT THE EDGES OF THE TOP SURFACE OF THE WINDING LEG FORMED BY SAID SPACED FIRST AND SECOND MAGNETIC CORE SECTIONS WHICH DEFINE A PORTION OF THE PERIMETER OF THE VERTICAL OPENINGS IN SAID FIRST AND SECOND MAGNETIC CORE SECTIONS. 